Ion gate method and apparatus

ABSTRACT

The present invention generally relates to systems and methods for transmitting beams of charged particles, and in particular to such systems and methods that employ defecting at least one set of grid elements into the same plane to form an ion gate. In addition, an operation method of closing a gate involving alternating voltages on the adjacent gate wires is described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. patentapplication Ser. No. 11/776,392, filed on Jul. 11, 2007, and is acontinuation in part of U.S. patent application Ser. No. 11/946,679,filed on Nov. 28, 2007, and claims the benefit of and priority tocorresponding U.S. Provisional Patent Application No. 61/170,628, filedApr. 19, 2009 respectively, the entire content of these cross-referencedapplications is herein incorporated by reference.

BACKGROUND OF THE INVENTION

Many analytical instruments, such as ion mobility spectrometers (IMS),can require a gating device for turning on and off a flowing stream ofions and/or other charged particles. IMS are widely used in fieldchemical analysis. IMS separate ionic species based on their ionmobility in a given media (either gas or liquid). Recent development ofthe IMS technology results in two forms of IMS instruments and systems.The time-of-flight (TOF) IMS separate ions based on their steady stateion mobilities under constant electric field. High resolving power withIMS has been achieved with the TOF-IMS instruments. Alternatively,devices that separate ions based their mobility changes under high fieldconditions, such as field asymmetric ion mobility spectrometer (FAIMS)or differential mobility spectrometer (DMS), can also be used.

Even though the gating device is a minor component in the overall designof an IMS, if manufactured correctly, this component can improve the IMSresolution and system performance. The gating device is used to regulatethe injection of ion packets into the analytical instrument. There aremany deficiencies with the current approaches for manufacturing gatingdevices.

SUMMARY OF THE INVENTION

The present invention generally relates to systems and methods fortransmitting beams of charged particles, and in particular to suchsystems and methods that employ defecting at least one set of gridelements into the same plane, such that the grid elements areinterleaved.

In one embodiment of the present invention, at least one electricallysubstrate (conducting or non-conducting) is used to deflect at least oneset of the grid elements into the same plane, such that the gridelements are interleaved. The ion gate has a first and second set ofelectrically isolated grid elements that lie in the same plane where therespective sets of grid elements are applied to alternate potentials.The advanced grid manufacturing methods and features are disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects, embodiments, and features of theinventions can be more fully understood from the following descriptionin conjunction with the accompanying drawings. In the drawings likereference characters generally refer to like features and structuralelements throughout the various figures. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the inventions.

FIG. 1 shows the completed ion gate from a front view;

FIG. 2 shows a cross-sectional top view of the ion gate;

FIGS. 3A and 3B show two different methods to deflect the grid elements;

FIG. 4 shows an alternative method to deflect the grid elements;

FIGS. 5A-5C illustrates the respective sets of gate elements;

FIG. 6 illustrates the process of manufacturing the ion gate;

FIG. 7A-7C shows the photo etched edges of the grid elements;

FIG. 8 schematically shows a construction of a Bradbury-Nielsen ion gateusing metalized dielectric rings and parallel wires;

FIG. 9 is a schematic example of a segmented Bradbury-Neilson gate; and

FIG. 10 illustrates an operation method of an ion gate.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The term ion mobility separator, and ion mobility spectrometer, and ionmobility based spectrometers are used interchangeably in this invention,often referred to as IMS, including time-of-flight (TOF) IMS,differential mobility spectrometers (DMS), field asymmetric ion mobilityspectrometers (FAIMS) and their derived forms. A time of flight ionmobility spectrometer and their derived forms refers to, in its broadestsense, any ion mobility based separation device that characterize ionsbased on their time of flight over a defined distance. A FAIMS, a DMS,and their derived forms separate ions based on their ion mobilitycharacteristics under high values of normalized electric field.

The systems and methods of the present inventions may make use of “drifttubes.” The term “drift tube” is used herein in accordance with theaccepted meaning of that term in the field of ion mobility spectrometry.A drift tube is a structure containing a neutral gas through which ionsare moved under the influence of an electrical field. It is to beunderstood that a “drift tube” does not need to be in the form of a tubeor cylinder. As understood in the art, a “drift tube” is not limited tothe circular or elliptical cross-sections found in a cylinder, but canhave any cross-sectional shape including, but not limited to, square,rectangular, circular, elliptical, semi-circular, triangular, etc. Inmany cases, a drift tube is also referred to the ion transportationand/or ion filter section of a FAIMS or DMS device.

Neutral gas is often referred to as a carrier gas, drift gas, buffergas, etc. and these terms are considered interchangeable herein. The gasis at a pressure such that the mean free path of the ion, or ions, ofinterest is less than the dimensions of the drift tube. That is the gaspressure is chosen for viscous flow. Under conditions of viscous flow ofa gas in a channel, conditions are such that the mean free path is verysmall compared with the transverse dimensions of the channel. At thesepressures the flow characteristics are determined mainly by collisionsbetween the gas molecules, i.e. the viscosity of the gas. The flow maybe laminar or turbulent. It is preferred that the pressure in the drifttube is high enough that ions will travel a negligible distance,relative to the longitudinal length of the drift tube, therefore asteady-state ion mobility is achieved.

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases.

Unless otherwise specified in this document the term “particle” isintended to mean chemical and/or biological single or plurality ofsub-atomic particle, atom, molecule, large or macro molecule,nanoparticle, or other matters that are vapor, droplets, aerosol,liquid, solid that follow a mobile medium, where the medium can be agas, a liquid, supercritical fluid and/or other fluidic materials.

The present invention generally relates to systems and methods fortransmitting beams of charged particles, and in particular to suchsystems and methods that employ defecting at least one set of gridelements into the same plane.

As used herein, the term “grid element” generally refers to wire, rod,cable, thin metal foil piece that can be planar, square, rectangular,circular, elliptical, semi-circular, triangular, but not limited tothese examples. The grid element can be made of any electricallyconducting material.

The term “gate element” generally refers to a structure that includesone or more grid elements that can be spatially arranged with a gapbetween each other.

One aspect of the invention relates to manufacturing an ion gate in sucha way that the ion gate can be produced in a simple, reproducible, andreliable manner. FIG. 6 illustrates a non-limiting process formanufacturing the ion gate. This method for manufacturing an ion gatefor a charged particle stream begins with the fabrication of the gateelements 603 and 607 that includes the grid elements. Each of the gateelements 603 and 607 are made so that the two different pairs of gridelements can be interleaved without contacting each other. Followed byassembling an insulating layer (electrically non-conductive, theinsulating layer can be any size and shape, such as a square or a diskwith openings, or a washer, that allows a different potential to thegate elements) 605 between the gate elements 603 and 607 to electricallyisolate the gate elements. The substrate throughout this patent istypically non-conducting, but can also be a conducting material for someapplications. Then two electrically non-conductive substrates 601 and609 are added to deflect the grid elements in the gate elements into thesame plane. FIG. 6 shows a non-limiting example, wherein twoelectrically non-conductive substrates are used. Similarly, oneelectrically non-conductive substrate can also be used to manufacturethe ion gate. Finally, the gate elements are secured together along withthe electrically non-conductive substrates and the insulating layer. Inan alternative embodiment, the gate elements can be segmented, thus eachsegment of the grid elements can be operated independently, i.e. openand close at different timing, as a segmented ion gate. The method formanufacturing an ion gate for a charged particle stream, can comprise ofelectrically isolated grid elements that lie in the same plane. Therespective sets of grid elements can be applied to alternate potentialsto close the gate and the same potential to open the gate. For example,the grid element is at 100 volts above and 100 volts below the referencepotential. The reference potential is the potential at the particularlocation of the gate in the drift tube. The steps used to manufacturethe ion gate can be in any order and comprise: fabricating at least twogate elements, wherein each gate element includes at least one set ofgrid elements; assembling an insulating layer between the gate elements;deflecting at least one set of grid elements into the same plane of theother set of grid elements with at least one substrate; and securing thegate elements and the non-conductive substrates together.

A non-limiting example of the completed ion gate is shown in FIG. 1. Theshape of the ion gate can be: square (shown), oval, circle, semicircle,triangle, rectangle, polygon, octagon, but not limited to theseexamples. FIG. 1 shows a front view of the completed ion gate. The iongate includes gate elements that contain the grid elements 103 are heldin place with several screws 105. The ion gate apparatus that is usedfor gating a charged particle stream comprises: at least two sets ofgrid elements that individual voltages can be applied to each set toopen and close; and at least one substrate for deflecting at least oneset of grid elements into the same plane of the other sets of gridelements. In addition an electrically insulating layer can be added toallow different voltages to be set to each set of grid elements.

Another aspect of the invention relates to providing an ion gate with aneffective gating function by applying a uniform tension on the gridelements, fabricating the gate elements such that the grid elements areequally spaced, and deflecting the grid elements into the same plane.

FIG. 2 shows a cross-sectional top view of the ion gate. Thecross-section shown in FIG. 2 is indicated in FIG. 1 with a cutting line107. The ion gate comprises a first and second electrically isolatedgate elements 204 and 206 that each have at least one grid element 205and 207. The electrically non-conductive or conductive substrate 208deflects the grid element 207 which is part of the gate element 206 intothe same plane as the deflected grid element 205 which is part of thegate element 204. The gate elements 204 and 206 are electricallyisolated by placing an insulating layer (electrically non-conductive orconductive) 210 between these gate elements. The grid elements aredeflected into the same plane 202 and are electrically isolated byinterleaving these sets of grid elements with a gap between each gridelement. FIG. 5C illustrates the respective sets of grid elements inFIG. 5A and FIG. 5B interleaved. In FIG. 2, the ion gate components aresecured together with a screw fastener 212. In this non-limitingexample, ether an electrically non-conducive material screw fastener maybe used or a conductive material fastener can be contained in anelectrically non-conductive standoff (not shown).

One embodiment of the present invention, involves using off-setelectrically non-conductive or conductive substrates to deflect the gridelements. FIG. 3A shows the electrically substrates 305 and 307 with nooff-set 301. FIG. 3B shows electrically substrates 305 and 307 with anoff-set 303. This off-set design may allow uniform deflection of gridelements and low cost manufacturing.

Another embodiment of the present invention, involves the shape of theelectrically non-conductive or conductive substrate to deflect the gridelements. The portion that deflects the grid element can be in the shapeof a wedge, hexagon, semi-circle, but not limited to these examples. Inaddition, the electrically non-conductive substrate portion thatdeflects the grid element can be independent to the secured electricallynon-conductive substrate. A non-limiting example is shown in FIG. 4,where a circular (not limited to only this shape) substrate 402 deflectsthe grid element and the secured substrate 404 holds the substrate 402in place.

Yet another embodiment of the present invention is the fabrication ofthe gate elements. The grid elements within the gate elements can beproduced by cutting, etching, evaporation or electroplating, but notlimited to these methods. In a non-limiting example, parallel rows ofgrid elements are formed by removing portions of a given thickness ofplanar metal foil by etching portions from the foil. This method forms aplurality of grid elements that are equally spaced. In addition toforming equally spaced grid elements within the gate element, the gridelements are made from the same gate element material as a singleentity. In this manner, the grid elements do not need to be fixed to thegate element through gluing (epoxy), glass soldering, or any otherattaching manner. Fabricating the gate elements by etching the gridelements is a robust and reproducible method for manufacturing the gridelements. In addition, since no gluing, soldering, or other attachingmanner is used in fabricating the gate elements, elevated temperaturesand/or thermal expansion of the grid elements are all uniform. The photochemical milling (etching) can be performed on one side or both sides ofthe material being etched.

FIG. 7A shows the shape (a pair of opposing concave fillets) of the gridelement etched on both sides of the material, etched from the top 701and the bottom 702 of the material. FIG. 7B shows the shape (a concavefillet) of the grid element etched on one side of the material, etchedfrom only the top side 704 of the material. The etched edge distance 703may be smaller or greater than the material thickness 705 depending onthe layout of the grid elements. For example, the etched edge distanceto the material thickness ratio is greater than zero, in particular1-50%, 50-100%, 100-500%. FIG. 7C shows three grid elements that areetched on both sides of the material. Photo chemical milling can produceuniform dimensions in grid element width 707 and gap 709 between gridelements forming a plurality of grid elements that are equally spaced.When the ion gate is a uniform product, injection of ion packets intothe drift tube are tight packets with limited background signal,therefore a higher signal to noise ratio can be achieved. In thisembodiment, regardless of manufacturing methods, the grid element is tobe made with a sharp edge, the geometry may generate a narrow gatingelectric field region resulting in high precision gating of chargeparticles. In an IMS device, a narrow ion pulse could be generated withprecision gate timing control. An ion gate apparatus for gating acharged particle stream comprises: at least two sets of electricallyinsulated grid elements on the same plane, the evenly spaced gridelements have at least one sharp edge face to adjacent grid element.

Another embodiment of the present invention is securing the gateelements together with non-conductive substrates and the insulatinglayer. The ion gate can be secured by clamping, soldering, screws, pins,but not limited to these examples. The insulating layer can be made fromany non-conductive material such as, ceramic, aluminum nitrate, but notlimited to these examples.

An alternative embodiment of manufacturing an “Tyndall” type of ion gatefor a charged particle stream involves two sets of electrically isolatedgrid elements, wherein the first set of grid elements is arranged withan offset in respect to the second set of the grid elements, such thatthe gaps of the first grid element is aligned with the second gridelements; each set of grid elements is applied to alternate potentialswhen the gate is closed and same potential when the gate is opened. Themethod involves the steps of: fabricating at least two gate elements byremoving portions of a substantially planar metal foil to form aplurality of grid elements; wherein each gate element includes at leastone set of grid elements; assembling an insulating layer between thegate elements; and securing the gate elements together.

In another embodiment of the invention, a metalized dielectric structureis used for the Bradbury-Nielsen gate. A ceramic material is coated withsingle or multiple layers of metallization materials. The metallizationprocess is commonly finished with a thin layer of nickel, gold or otherinert metal for enhanced chemical resistivity. FIG. 8 shows a uniqueconstruction method of a Bradbury-Nielsen ion gate using a metalizedceramic material. It is built with a frame ring, a tension ring 802 andparallel wires 805 that are pre-winded on a metal frame. One or therings, either the frame ring or the tension ring is metalized 815 with apattern 810 that connects every other wire to each other. In oneembodiment, the frame ring has metalized contacts 807 that are 1 mmapart (center to center). During the ion gate construction, the parallelwires are lined up with these contacts and form a firm contact while thetension ring is pushed down into the frame ring. As the wire is selectedto match the thermal expansion of the frame ring and tension ring, thewires can be maintained parallel while the IMS is operated underdifferent temperature conditions. The gate control voltage(s) areapplied to the wires by attaching an electrical lead to the contactpoint that is on the outside of the frame ring. Not only for metalizedceramic tube IMS design, the Bradbury-Nielsen ion gate can be used forother analytical instruments.

In various embodiments for symmetric IMS, an ion focusing method can beemployed to guide ions to a target collection area on the collector.Suitable focusing methods may include, but are not limited to, staticelectric field focusing and ion funnel focusing. An ion collector can besegmented to facilitate, collection of ions with specific ion mobility(drift time) or a certain range of mobilities on to different segment ofthe ion collectors. A segmented Bradbury-Nielson gate can be used toenhance the separation and collection.

In various embodiments of IMS instruments, wherein the Bradbury-Nielsongate can be segmented. A variety of geometries, including but notlimited to parallel, rectangular, concentric ring shape, can be used forthe segmentation, referring to FIG. 9, various embodiments can useparallel segmentation. Each segment of the ion gate, for example, 901,903, and 905, can be controlled to open at a different time. Such asegmented ion gate can be used as either first or second ion gate in atime-of-flight type ion mobility separator. While it is used as thesecond ion gate in a IMS, multiple portions of ions with different drifttime are allow to pass through segmented ion gate, thus collected ondifferent sections of ion collectors, and recovered separately ifdesired.

In various embodiments, an apparatus of ion gate for an ion mobilityseparator comprising a segmented Bradbury-Nielson that contains multiplesections of Bradbury-Nielson gate. The segmented Bradbury-Nielson gatecan be used as a second gate in a time-of-flight type ion mobilityseparator. The segmented Bradbury-Nielson gate comprises a variety ofgeometries which may include but is not limited to: parallel,rectangular, concentric. The ion mobility separator further comprises asegmented ion collector where a plurality of sections of ion collectoris inline with the sections of the segmented Bradbury-Nielson gate.

This invention further describes a method and apparatus of ion gateoperation. In one embodiment, an AC voltage is used to close the gate.In a common operation of the Bradbury-Nielson gate, the ion gate is openwhen the adjacent grid elements are at the same potential and the iongate is closed when a DC voltage, e.g. 30V, 50V, 100V, 200V, or −30V,−50V, −100V, −200V are applied on the adjacent grid elements. Thevoltage creates an electric field that pushes ions toward the gridelement that is a lower potential, thus preventing ions from penetratingthrough the ion gate when closed.

During ion mobility measurements, the ion gate is opened for a shortperiod of time, e.g. 100 microseconds, and then closed for a period oftime, e.g. 20 millisecond, while ions are traveling in the drift tube.FIG. 10 illustrates a closed ion gate. When the applied voltage ishigher than the reference potential, a ‘+’ is shown for the gate wire(i.e. grid element) and when the applied voltage is lower than thereference potential, a ‘−’ is shown for the gate wire. The voltagedifference between the adjacent wires causes positive ions to becollected on the (−) wire and negative ions to be collected on the (+)wire. By repeating wire layout pattern of (+) and (−) wires, a largearea is covered and ions are prevented to pass through the ion gate. Inthis embodiment, an AC voltage instead of DC voltage is applied the gatewires. In this case, the potential of each wire is constantly changing.The potential on wire 1003 is ‘+’ and wire 1004 is ‘−’ at the state1001, and then the potential on wire 1003 is ‘−’ and wire 1004 is ‘+’ atthe state 1002. The state 1001 and 1002 repeats at certain frequency.The voltage and frequency of the AC applied to the adjacent wires isoptimized to completely close the ion gate. The ion gate is opened bysetting all gate wires at the same potential. The new gate configurationand operational method is not limited to be used for ion mobilityspectrometer, but can be used for any device that needs to shut off astream of charged particles.

In a variety of the embodiments, a method for operating an ion gate fora charged particle stream involves opening the ion gate by settingadjacent gate wires (grid elements) at the same potential; closing theion gate by setting adjacent gate wires at different potentials byapplying an AC voltage to the adjacent wires. The AC voltage can becontrolled to provide a given frequency and amplitude that that is mostsuitable for the intended operation. The frequency can be a constantand/or controlled to cover a broad range during a period when the iongate is closed. Similarly, the amplitude can be a constant and/orcontrolled in a range during a period of closing the gate. The ACvoltage may be a symmetric or asymmetric waveform. In a variety ofoperation modes, the AC powered ion gate can be operated as such,conducting a series of ion mobility measurements under a series ofdifferent frequencies and/or amplitudes, and then integrating the seriesof ion mobility measurement data into an ion mobility spectrum usingcommon data processing algorithms, such as summing.

Even though many embodiments and examples given in this disclosure referto ion gate for general IMS device, these devices can be operated underlow vacuum, ambient or high pressure conditions. Alternatively, the iongate can be operated in liquid for liquid phase IMS or other devices,such as electrophoretic devices, where packets of ions need to beformed. The ion gate can also be used under vacuum conditions forgenerating ion packets for mass spectrometers, such as a time of flightmass spectrometer. This invention discloses gating methods andapparatuses that can be used for any device where packets of chargedparticles need to be formed.

It is recognized that modifications and variations of the inventiondisclosed herein will be apparent to those of ordinary skill in the artand it is intended that all such modifications and variations beincluded with the scope of the appended claims.

What is claimed is:
 1. A method for manufacturing an ion gate for acharged particle stream, comprising electrically isolated grid elementsthat lie in the same plane, the method comprising the steps of: a.fabricating at least two gate elements, wherein each gate elementincludes at least one set of grid elements; and wherein fabricating thegate element includes removing portions of a substantially planar metalfoil to form a plurality of grid elements; b. assembling an insulatinglayer between the gate elements; c. bending at least one set of gridelements into substantially the same plane of the other set of gridelements with at least one substrate; and d. securing the gate elementsand the substrates together.
 2. The method of claim 1, wherein removingportions of the substantially planar metal foil to form the plurality ofgrid elements includes etching portions from the foil.
 3. The method ofclaim 2, wherein etching portions from the foil includes etching fromone or both sides of the material.
 4. The method of claim 1, whereindeflecting the grid elements into the same plane includes interleavingthe grid elements.
 5. The method of claim 1, wherein fabricating thegate elements includes spacing the grid elements equally.
 6. The methodof claim 1, wherein fabricating the substrates includes coating aceramic material with single or multiple layers of metallizationmaterials.